Group III-V compound semiconductors such as, for example, GaN and AlGaN, are widely used for optoelectronics, electronic devices and the like, owing to many advantages such as, for example, a wide and easily adjustable band gap energy.
In particular, light-emitting elements such as light-emitting diodes or laser diodes using group III-V or II-VI compound semiconductors may realize various colors of light such as, for example, red, green, and blue light, as well as ultraviolet light, via the development of device materials and thin-film growth technique, and may also realize white light having high luminous efficacy via the use of a fluorescent material or by combining colors. These light-emitting elements have advantages of low power consumption, a semi-permanent lifespan, fast response speed, good safety, and eco-friendly properties compared to existing light sources such as, for example, fluorescent lamps and incandescent lamps.
Accordingly, the application of light-emitting elements has been expanded to a transmission module of an optical communication apparatus, a light-emitting diode backlight, which may substitute for a cold cathode fluorescent lamp (CCFL) constituting a backlight of a liquid crystal display (LCD) apparatus, a white light-emitting diode lighting apparatus, which may substitute for a fluorescent lamp or an incandescent bulb, a vehicle headlight, and a signal lamp.
A molding part may be disposed around a light-emitting element to protect, for example, a light-emitting structure or wires. Since light is refracted when passing through the molding part, which is formed of, for example, silicon, the molding part may serve as a primary lens.
However, when the light-emitting element is used as a light source of a lighting apparatus, a secondary lens may be used in order to adjust the path along which light is emitted. The aforementioned secondary lens is commonly referred to as a “lens”.
An optical path may be changed depending on the material of the lens and particularly on the shape thereof. In particular, in an application in which the light emitted from the light source needs to be directed in a specific direction such as, for example, forward or rearward, the shape of the lens is of increased importance.
Based on the shape of the lens, a beam angle or a field angle, which corresponds to the distribution of light emitted from a light-emitting element module including the lens, may be determined. The light emitted from the light-emitting element module may have various intensity distributions depending on the angle. Although the beam angle, which represents the range of distribution of light having intensity of half or more the maximum intensity, is very important, the field angle, which represents the range of distribution of light having intensity of one tenth or more the maximum intensity, is also important.
When the field angle is excessively wide, the light from the light-emitting element module is emitted to an excessively wide range, which may deteriorate luminous efficacy.